LM8207MTX/NOPB National Semiconductor, LM8207MTX/NOPB Datasheet - Page 12

• Manufacturer Part Number: LM8207MTX/NOPB
• Description: IC BUFFER/DVR/VREF 48-TSSOP
• Manufacturer: National Semiconductor

Specifications of LM8207MTX/NOPB

• Applications: TFT-LCD Panels: Gamma Buffer, VCOM Driver
• Output Type: Rail-to-Rail
• Number Of Circuits: 18
• -3db Bandwidth: 2MHz
• Slew Rate: 1 V/µs
• Current - Supply: 6.5mA
• Current - Output / Channel: 50mA
• Voltage - Supply, Single/dual (±): 6 V ~ 16 V
• Mounting Type: Surface Mount
• Package / Case: 48-TFSOP (0.240", 6.10mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LM8207MTX

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Application Section
Figure 3 shows how the display information is refreshed.
Using the row and column drivers, one pixel is addressed at
the display. The column driver receives the digital color data
from the timing controller. The corresponding gamma volt-
age will be determined, using the gamma correction curve.
In fact, the gamma correction curve is just a voltage refer-
ence with 18 output tabs, which presets the color intensity
settings. This gamma voltage is written to the pixel. The
column driver selects one column at the time; the changing
in the load may affect the ‘tabs’ of the gamma correction
curve. This problem can be solved using ‘gamma buffers’ to
isolate the gamma correction curve from the column driver.
PRINCIPLE OPERATION of the LM8207
The LM8207 combines three basic functions used in TFT
displays:
• Voltage Reference
• Gamma Buffers
To improve picture quality and to reduce brightness varia-
tions, a highly stable reference voltage is available. It has
a low drift over the operation temperature range. This
output voltage (OUT_V
voltage to define the gamma correction values.
The gamma correction curve can be defined easily using
an external chain of precision resistors. To ensure load
independent gamma correction levels, 18 gamma buff-
ers, each having a low output resistance, can be used to
drive the TFT display column drivers.
REF
) is used as the reference
(Continued)
FIGURE 3. Block Diagram of a Typical TFT-LCD
12
• V
These three functions are discussed in detail in the following
sections.
VOLTAGE REFERENCE
The internal Voltage Reference of the LM8207 can be used
to improve picture stability. This accurate reference is highly
stable over the operation temperature range. The output
voltage (OUT_V
using two external resistors. In the next two sections, the
possibilities for setting the output voltage of the Voltage
Reference and the operating range of the Voltage Reference
are discussed.
SETTING THE OUTPUT VOLTAGE OF THE VOLTAGE
REFERENCE
The output voltage of the Voltage Reference Amplifier
(OUT_V
bination with the internal amplifier and two external resistors.
In Figure 4 a typical application circuit for V
The V
applied to the back plate of all the pixels. Writing color
information to all the pixels will cause high current varia-
tions at the V
driving large output currents.
COM
REF
Buffer
COM
) can be set using the internal reference in com-
buffer supplies a common voltage, which is
COM
REF
) of the Voltage Reference can be set
level so this V
COM
buffer is designed for
REF
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is given.